1. Field of the Invention
This invention relates generally to a millimeter-wave camera providing both scene imaging and communications and, more particularly, to a millimeter-wave camera that passively receives millimeter-wave radiation from a scene, and demodulates transmitted signals within the scene to provide transmitter location and communications at millimeter-wave frequencies.
2. Discussion of the Related Art
Millimeter-wave cameras are known in the art that passively detect millimeter-wave radiation (30-300 GHz) emitted by objects in a scene. Passive detection of millimeter-wave radiation for imaging purposes provides certain advantages over other types of imaging systems that detect visible light, infrared radiation or other electro-optical radiation. These advantages are available because millimeter-wave radiation is able to penetrate low visibility and obscured atmospheric conditions caused by many factors, including clouds, fog, haze, rain, dust, smoke, sandstorms, etc., without significant attenuation, as would occur with other types of radiation. More particularly, certain propagation wavelengths in the millimeter-wave spectrum, such as W-band wavelengths in the atmospheric window around 94 GHz, are not significantly attenuated by oxygen and water vapor in, air. Millimeter-wave radiation is also effective in passing through certain hard substances, such as wood and drywall, to provide imaging capability through walls. Thus, millimeter-wave imaging is desirable for many application, such as aircraft landing, collision avoidance and detection systems, detection and tracking systems, surveillance systems, etc. Virtually any type of imaging system that can benefit by providing quality images under low visibility conditions can benefit using millimeter-wave imaging.
Millimeter-wave imaging systems that employ a focal plane array to detect millimeter-wave radiation in a scene are known in the art. For example, a passive millimeter-wave camera (PMMC) for many applications is available from TRW. Individual millimeter-wave receivers make up the focal plane array, where each receiver includes a millimeter-wave antenna and detector circuitry. An array interface multiplexer is employed that multiplexes the electrical signals from each of the receivers to a signal processing system.
A millimeter-wave imaging system employing a focal plane imaging array of this type is disclosed in U.S. Pat. No. 5,438,336 issued to Lee et al., titled xe2x80x9cFocal Plane Imaging Array with Internal Calibration Source,xe2x80x9d assigned to the Assignee this application, and herein incorporated by reference. The system includes an optical lens that focuses millimeter-wave radiation collected from a scene onto an array of pixel-element receivers positioned in the focal plane of the lens. Each pixel element receiver includes an antenna that receives the millimeter-wave radiation, a low noise amplifier that amplifies the received millimeter-wave signal, a band pass filter that filters the received signal to only pass millimeter-wave radiation of a predetermined wavelength, and a diode integration detector that detects the millimeter-wave radiation and generates an electrical signal. The signal from each diode detector is then sent to an array interface unit that multiplexes the electrical signals to a central processing unit to be displayed on a suitable display unit. Each pixel element receiver includes a calibration circuit to provide a background reference signal to the detector.
In accordance with the teachings of the present invention, an imaging and communications system is disclosed that includes a passive millimeter-wave camera employing a focal plane array of millimeter-wave integrated circuit receivers. The camera images a scene that may include one or more beacons. The beacons transmit millimeter-wave signals that are modulated by a suitable modulation device so that the beacons can provide communications signals. The receivers in the camera employ a demodulator to demodulate the detected millimeter-wave signals from the scene. Therefore, not only does the camera image the beacons in the scene to provide beacon location, but also can separate and decipher communications signals from the beacons. Thus, the camera provides a gray-scale image of the scene identifying the location of the beacons and a decoded image of the scene to separately identify and/or communicate with each beacon.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.